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moment diagram and the process re- peated until requisite strength is pro- vided at every section:on the dock. These calculations are made for every loading and every condition to which the dock may be subjected and at every point where the section under- goes appreciable change. Touching the question of the tow- ing of docks, and especially the tow- ing of the "Dewey," to which the author refers, it would seem that the history of that expedition indicates that its frequent breaking adrift was the result of trying to make too much speed under adverse weather condi- tions and using too short a tow line. All the mishaps occurred during the first half of the voyage, and, as experience was gained and _ possibili- ties realized, such occurrences ceased. In the opinion of the speaker, the best results in towing a floating dock will be obtained by the use of the longest tow-line that can be handled and by accommodating the speed to weather conditions. It is certainly better to -make no . headway at all, 'or. even some leeway, than to part a tow-line. By using one vessel of sufficient weight and power to do the towing, the strain on the tow- line may be quickly regulated and maneuvering may be simplified. Model tank experiments with dock models would, in all probability, be productive of much information bear- ing on the proper shape of the under- water body for a practical minimum of towing resistance. While the mo- bility of the floating dock is a dis- tinct advantage, it must be remem- bered that speed and towing qualities are of only secondary importance as compared with its adaptability to the docking of ships, but wherever the, design can be so developed as to pro- vide for the docking qualities and at the same time improve the towing qualities without prohibitive increase in cost, it should be done by all means. To accomplish this the speak- er, some years ago, recommended that nontoons of floating docks be given sco ends. Pointed or bow ends for docks were not recommended by members of the firm which towed the Algiers dock to its destination, all of whom were experienced tow masters and alli of whom accompanied the expedition. It was stated that the dock was seldom pointed fair to its bridle after leaving the Virginia capes,--in fact members of the expedition aver that both leads of the bridle were usually sawing away on the same side fender. - The opinion of Mr. H. T. Hansson, who accompanied the Dewey expedi- tion is thus expressed: © TAFE MARINE. Review "It would, without doubt, greatly reduce the towing resistance if the ends were given some less resistant shape than square, and the writer thinks the scow shape would be pref- erable to the pointed ends sometimes used on docks. A floating dock will always make an angle with the course in 'any wind as long as it is not from dead ahead, so that, if a dock has pointed ends, the sides of these would always be more or less equare against the direction in which the dock is moving, whereas, if the ends are scow-shaped, the angle would al- ways remain the same, besides which, the scow shape has the advantage of. not reducing the deék area, as would be the case with pointed ends." With the author's remarks on the durability of steel floating docks, the - writer of this discussion is in hearty accord. No reliance can be placed in weathering, scraping or brushing, for the removal of scale, and there can be no doubt as to the ultimate economy of pickling. The Vice President: If there is no further discussion, I will call on Mr. Roberts to close the discussion. Mr. T. G. Roberts: First answer- ing Mr. Chace's question, he asked why the Pensacola dock broke in two. The Pensacola dock has five pontoons--it has openings the same. (Mr. Roberts then drew a diagram on the blackboard). These are the five pontoons (the subsequent design having three pontoons, which is a better design). This break between the docks is a disconnection of all the bolts. Between that line and that line, all the stiffness of these braces, there is a break between this in- terim, and also at the inner edge of this, and of course, the maximum moment coming in the center of the dock, and increasing near the center, and being greater over here it was exactly in this section that the Pensa- cola dock broke. There was an in- vestigation at the time, and various people had to do with the dock, stated that, this dock, which was de- signed by Clark & Stanfield, in Eng- land, and which was sold to the Unit- ed States government--the old Ha- vana dock, 10,000-ton dock, and brought to Pensacola--that great economy had been used in its manu- facture, and the plates were too thick. The investigation brought out that at the time of the self-docking of this dock, two end pontoons had been dis- connected, and the dock lowered, and then connected at a higher level, and for some reason or other the dock master failed to open the valves, when he was leaving, and the flowing 31 water, exceeding the running out, let in to such an extent, arid the™ force being exerted at the end tended to break the dock, and there were several causes which led to the break. That is where the break occurred (in- dicating on the blackboard), and that is what designers are looking out for. I do not think the design will ever be repeated. Mr. Chace has seen this dock at New Orleans, he was there for a visit. while I had charge of it. In the Dewey a different arrange- ment has been made--instead of hav- ing about 4,000 bolts to connect and disconnect on either side, while you are self-docking a dock is made in that shape, with the side pontoons continuous on both sides, and also through the center, this portion and these two ends are made so that the dock is in its normal position, that is the shape it takes, and when they wish to self-dock they raise this por- tion and go inside of that portion, and this portion helps that portion up. When this portion is desired to be docked, they pump this as high as they can, and flood this, and lower that, and bring them down into that position, and then pump up and raise this portion of the dock, with these two portions. 1 think that is the best invention for docks ever in- vented.. It was done by Mr. Hans- com, and I understand he worked it out from the model, and saved himself a great deal of. figuring any. formula scale like this. As to pickling, this New Orleans dock was the first dock to be an- chored in fresh water, and there were various theories, not only about de- terioration, but also painting, and actual practice. Why that dock was. not pickled I do not know exactly, but it was: not, bur the' actual ex- perience shows it should have been, and the government is cognizant of that,-and | 'am «sure that fe error will not be repeated. Also, for some reason, the Dewey dock was _ not pickled, and I do not know what the experience was for that dock. I know it is the intention of the government to pickle these docks, as the cor- rosion takes place very rapidly in spots all over the dock; that is, the wetted surface of the dock. The experience in regard to paint- ing has borne out that in the fresh water the paint does not last any longer than in salt water. People ar- gued that the dock being in fresh water would not require to be re- painted, not perhaps for 20 years. That is all wrong. With regard to the question asked by Prof. Peabody, that is a question ea ea MK inky Rega